The next-generation mobile network system EPC is a network architecture that accommodates 3G (third generation mobile phone communication system), LTE and so forth in one network. The following describes several network nodes.
A MME is a mobility management node. In LTE radio access, the MME takes charge of mobility management (mobility control), such as tracking, of an idle-mode mobile station (UE), authentication and setting up a user data forwarding path between an S-GW and a base station (eNodeB), in LTE radio access. The mobile station (UE) is also termed ‘a user apparatus’, ‘a mobile terminal’ or simply ‘a terminal’. The MME is involved in tracking and paging of idle-mode UEs or in bearer activate/deactivate processes. The MME selects the S-GW at the time of handover of the UE in LTE and performs user authentication along with HSS. It is noted that a bearer means a logical packet transmission path set up between eNodeB and S-GW/P-GW or the like.
An SGSN is a mobility management node in the 3G core network. It is a packet switching unit that takes charge of mobility management for the UEs, such as serving subscriber management, serving subscriber mobility management, originating/incoming call control, tunneling control, charging control, QoS (Quality of Service) control or the like.
When the UE is in an idle or power-saving state (LTE-idle) in an LTE core network, the UE is identified at the accuracy corresponding to a tracking area list (TA List) composed of a plurality of cells (MME maintains the latest updated TA List). At the time of an incoming call to the mobile station, paging is performed using the latest TA List registered last time. The SGSN of the 3G core network performs paging in an RA (Routing Area).
An S-GW performs routing and forwarding of a user data packet. The S-GW is a bearer management node that manages context of the UE (a parameter of IP bearer service or the like). In response to a bearer setting request from an MME that has received an attach request from the UE, The S-GW sets a path setting request for a P-GW and bearer in the direction of an eNode. The S-GW also performs triggering of a paging when the downlink (DL) data to a terminal has arrived.
A P-GW takes charge of connection of the UE to a packet data network (a service network: Web browsing service or an external work, such as IMS or the like.
The following describes restarting of MME/SGSN.
The ‘restart’ or ‘restart of MME/SGSN’ means cessation of service due to failure, or intentional cessation of service for maintenance, that leads to initialization setting operation in the MME/SGSN, as a result of which, subscriber information or bearer information that is necessary for the MME/SGSN operation to operate is lost.
Non-Patent Document 2 (3GPP TS 23.007) provides that, when the S-GW detects that the MME/SGSN has restarted, the S-GW is to release bearer context of the UE registered in the MME/SGSN that has restarted. That is, According to Non-Patent Document 2, when the MME re-starts after failure, the MME removes the entirety of hearer contexts affected by the restarting. When the S-GW detects that the MME has restarted, the S-GW removes PDN connection table/bearer context corresponding to the MME that has restarted and releases inner resources relevant to the PND connection.
Assuming that an S-GW operates in accordance with the above specification of the Non-Patent Document 2, when the MME operation has restarted, the S-GW is unable to effect a packet incoming operation to the UE until originating a call by the mobile station itself or periodic location registration (e.g., Attach/TAU Request) periodically by performed by the UE itself to the MME.
When there is an incoming call to the UE, the network performs paging all at once to whole cells associated with an area where the UE has made location registration (tracking area). The so paged UE accesses a serving cell and establishes a call. However, according to the specification of Non-Patent Document 2, the entirety of hearer information or resources of the restarted MME has already been removed or released. That is, in the S-GW, radio access hearers in the direction of from the S-GW to the eNodeB and session information between the MME and the S-GW have been removed or released, so that when the incoming packet data to the UE is received only to no effect.
In the S-GW in this state, TEID or GRE Key, as the identification information of a tunnel (GTP-U or P-MIP), a transport protocol between the S-GW and the P-GW, also has been removed. Hence, in the S-GW, the incoming data is rejected. The P-GW also removes relevant resources in response to the rejection of the incoming packet data from the S-GW.